Prior art displays are often overwhelmed (“washed out”) in high ambient light conditions and thus are not visible to a user. A common example of this is a laptop computer LCD display which utilizes a backlight to illuminate a LCD panel. This works effectively when the LCD backlight is brighter than the ambient light that shines on the LCD. However, due to packaging and battery life constraints, the typical laptop LCD backlight is not bright enough to overcome high levels of ambient light, such as direct sunlight, and the display becomes unreadable in these conditions. Further, prior art displays often require high capacity power sources to operate, and prior art mobile displays are often inconvenient to use, especially while performing a concurrent task.
Portable electronic devices such as electronic multimeters, mobile phones, portable music players, handheld GPS units, and others bring many conveniences to their users. However, a major disadvantage of such devices is that their displays (which provide data critical to their operation) typically reside solely on the device. This means that when the user wishes to read information off of the device, the user is required to physically move the device into the user's field of view. This requirement can be very inconvenient when the user is wearing the device (e.g., on a belt clip) or when the user has the device in a pocket. This requirement can also be very inconvenient and even dangerous when the user has his hands otherwise occupied and/or is simultaneously performing a task that is visually intensive (e.g., driving, cycling, inspecting, and performing construction or repair work). Enabling visual information from these pre-existing devices to be seen in a user's line of sight would increase both safety and convenience.
Head mounted displays have been devised to lessen the inconvenience related with some mobile displays; but head mounted displays are only available for a small range of devices and uses. Generally, prior art head mounted displays are one of two types: unwired battery powered head mounted displays (for maintenance work or entertainment, for example) and wired head mounted displays that do not rely on their own power sources (military-type displays that deliver information to pilots, for example). Both have important limitations associated with use in high ambient light conditions, including the “washing out” problem noted above.
In addition, prior art unwired battery powered head mounted displays require a significant amount of power to illuminate the displays, and thus must include powerful batteries. This requirement for power can significantly add to the display's cost, size, and weight, as larger and/or more expensive batteries are required or more powerful artificial light sources are used. Alternately, this power requirement can reduce the total operating time available to the user, which reduces the usefulness of the displays.
Prior art wired head mounted displays generally operate from larger power sources accessed through the wires and do not suffer the need for strict power conservation. However, they can still benefit from the use of smaller, less powerful artificial light sources or from the outright elimination of artificial light sources in order to reduce weight, size, cost, and/or power consumption.